Antenna



Patented May 24, 1938 UNITED STATES 2,118,429 ANTENNA William S.-Dut-tera, Lynbrook, N. Y., assignor to' Radio Corporation of America, acorporation of Delaware Application April 16, 1937, Serial No. 137,178

6 Claims.

tower type, and has for its primary object to provide a, simple and lesscostly antenna for reducing high angle radiation than antenna structureshitherto proposed for this purpose.

The useful range of radio transmission on many frequencies, especiallythose of broadcast service, is unduly limited atnight time by fadingwhich often causes distortion. This fading which occurs at a relativelynearby point, is caused by reflection of the high angle radiation fromthe ionized layer of atmosphere. The reflected ray or rays arrive atthis nearby point and by interference with the ground wave cause fadingand distortion. It is known that high angle radiation can'be reducedeither by building an antenna sufiiciently high so that the naturalcurrent distribution results in a reduction of the high angle radiation,or by producing a suitable artificial current distribution in a shorterantenna, as by employing a capacity and tuning coil arrangement at thetop of an antenna. Because of the cost of building an antenna to theoptimum height for least high angle radiation, and the mechanicaldrawbacks of such a tall structure, the tendency is toward a shorterantenna which will produce some of the results obtained from the largerstructure.

Another disadvantage in known antenna structures where a capacity topand tuning coilarrangement is used, or where a sectionalized antenna isused with a tuning coil electrically coupling the sections together, forpurposes of reducing high angle radiation, lies in the existence ofcomparatively high voltages across the tuning equipment of the antennaatthe sectionalized' point, when high power is used.

The foregoing disadvantages of antenna structures as heretoforeconstructed, are largely overcome in the antenna structure of thepresent invention. The invention consists essentially in the provisionof a relatively short sectionalized r transmitting antenna having acurrent reversal in the two sections of the antenna. The bottom sectionof the antenna is excited in such phase and amplitude that the radiationtherefrom materially reduces the ratio of high angle to ground waveradiation emanating from the antenna.

Other objects, features and advantages will appear hereinafter from areading of the following description taken in conjunction with theaccompanying drawing, wherein:

Fig. 1 is a view in side elevation of a vertical sectionalized antennaconstructed in accordance with the present invention;

Fig. 2 shows the general shape of the current distribution in theantenna of Fig. 1 when enervgized in accordance with the principles ofthe 5 invention; and I Fig. 3 is a detail of one type of suitablenetwork, given by way of example only, which can be inserted between thetransmission line and the two sections of the antenna for obtaining thedesired phase and amplitude relations of the currents in the twosections of the antenna.

In Fig. 1 there is shown a sectionalized tower structure, whose topsection I has the general dimension A, and whose lower section 2 has thegeneral smaller dimension B. The lower section 2 is insulated from thetop section I and may be insulated from ground by means of suitableinsulators 3, 3. Although the antenna has been shown of theself-supporting type formed of struc- 2O tural steel members andreinforcing struts and girders, it may, if desired, be a verticaltubular mast, with or without guy wires, or even a straight aerial Wire.The dimensions of sections 1 and 2 are not critical, the length of thetop section being at least twice that of the lower section. As anillustration of one particular type of antenna, the ratio of the heightof section i to that of section 2 may be of theorder of 5: 1. Theoverall length of the antenna structure should be less than 200electrical degrees at the operating frequency.

It is essential in the practice of the; invention that the sections land 2 be energized with ourrents'of opposite phase. This maybe suitably.eifected by means of a concentric transmission line such as 4 feedingthe lower section 2 at its upper part and the top section I at its lowerpart, through a suitable network 6, as shown. Where a coneentr'ienne isused,'th'e' outer tubular conductor is connected to one input terminalof the network, while the inner conductor is connected to the otherinput terminal of the network, the two output terminals being connectedthrough suitable leads such as 5 to the sections of the antenna. Theseleads 5 are preferably soldered or welded to the tower members. Network6 is herein shown mounted within the antenna structure on a suitableplatform of any desired type.

One suitable type of network which can be used to give the desiredcurrent distribution of Fig. 2- is shown in Fig. 3. This networkprovides an adjustment of the ratio of currentsli and I2 in the twosections of the antenna and gives a phase difference between thecurrents I1 and I2 of the 55 order of 180. In other words, the currentsI1 and I2 are of substantially opposite phase and flow in oppositedirections in the tower. By proper choice of the amplitudes and thephase angle between currents I1 and I2 as effected by the adjustment ofcapacitors and inductors in the network 6, the high angle radiation fromthe antenna is reduced, and by keeping the energy losses low, the groundsignal is increased. Optimum adjustment of the antenna may be obtainedby observing fading at a distant point or points while the abovementioned changes are made.

Although the sections I and 2 of the antenna have been shownsectionalized at a feeding point which coincides with the currentreversal location, it should be understood that the invention is notlimited thereto inasmuch as the lower section 2 can be excited at thebase near the ground, while the upper section I can be excited at thepoint shown or at a higher location, the essential requirement beingthat both sections be separately fed in order to obtain the desiredrelationship between the currents in the two sec tions. These currentsin the two sections should be of substantially opposite phase and ofproper relative magnitude to efiect the desired reduction in high angleradiation.

It will be obvious, of course, that the invention is not limited to theparticular type of network shown since any other suitable arrangementfor achieving the desired result may be employed, whether this networkemploys concentrated reactances or reactances of substantially uniformlydistributed constants. Nor is the invention limited to any particularlocation for this network inasmuch as it may be located near the groundor outside the antenna structure. Furthermore, the side elevation ofFig. 1 is intended to typify a tower structure of any suit able designsuch as the four-leg or three-leg, or single leg, either self-supportingor guyed tower, and a tower with or without a tapered cross section.

What is claimed is:

1. A vertical antenna structure having an overall length less than 200at the operating frequency and including two vertical adjacent sectionsof unequal lengths insulated from each other, said sections being devoidof concentrated reactance, the upper section having a length at leasttwice as long as the lower section, and means for individualy energizingsaid sections in such manner that the currents in said sections aresubstantially of opposite phase and of relative magnitude sufiicient toreduce high angle radiation.

2. A vertical sectionalized antenna comprising an upper section and anadjacent lower section,

said upper section being longer than said lower section, insulatorsbetween said sections for insulating said sections from one another,feeding means for individually exciting said sections, a network ofcapacitance and inductance located between at least one of said sectionsand said feeding means, said network being so adjusted as to produce insaid sections currents of substantially opposite phase and of suchmagnitude as to reduce high angle radiation.

3. A vertical sectionalized transmitting antenna including two adjacentsections of unequal lengths, the upper one of which is longer than thelower one, means for insulating said sections from each other, aconcentric transmission line, conductors individually extending fromsaid sections to said transmission line, and a network of inductance andcapacitance located between said conductors and said line, said networkbeing adjusted to produce in said sections currents of substantiallyopposite phase and of proper magnitude to reduce high angle radiation.

4. An antenna system in accordance with claim 3, characterized in thisthat said'antenna is of the self-supporting type formed of structuresteel members and reinforcing struts, and said network is mounted withinthe structure of said antenna and near the upper part of said lowersection.

5. A transmitting antenna including two vertical adjacent sections ofunequal lengths, the upper section having a length longer than the lowersection, insulators between said sections for insulating said sectionsfrom each other, a concentric transmission line feeder extending upwarda substantial portion of the length of said lower section, leadsindividually connecting the lower part of said upper section and theupper part of said lower section to said transmission line, a networklocated between said leads and said transmission line, said networkbeing adjusted such that the currents in the upper and lower sectionsare of substantially opposite phase and proper magnitude to reduce highangle radiation.

6. A vertical sectionalized antenna comprising an upper section and anadjacent lower section, said upper section being at least twice as longas said lower section, insulators between said sections for insulatingsaid sections from one another, feeding means for individually excitingsaid sections, a network of capacitance and inductance located betweenat least one of said sections and said feeding means, said network beingso adjusted as to produce in said sections currents of substantiallyopposite phase and of such magnitude as to reduce high angle radiation.

WILLIAM S. DU'I'TERA.

